Saturation of open-circuit voltage at higher light intensity caused by interfacial defects and nonradiative recombination losses in perovskite solar cells

Perovskite solar cells are a type of solar cell that utilizes perovskite materials as the active layer to convert sunlight into electricity. Perovskite solar cells have gained significant attention in recent years due to their remarkable efficiency and potential for low-cost production. They offer several advantages over traditional silicon-based solar cells. One of the main advantages is that perovskite materials can be manufactured using low-cost solution-based processes, making them more affordable and accessible. Additionally, perovskite solar cells have demonstrated high power conversion efficiencies, reaching levels comparable to or even surpassing those of silicon solar cells.  Perovskite solar cells have shown rapid progress in efficiency improvements over a relatively short period of time. However, there are still challenges that need to be addressed for their widespread commercialization. One major challenge is the stability of perovskite materials, particularly in the presence of moisture and heat. Efforts are underway to develop more stable perovskite formulations and encapsulation techniques to enhance their durability. Researchers and scientists are actively exploring various strategies to further enhance the performance of perovskite solar cells. This includes optimizing the composition and structure of perovskite materials, improving charge transport and extraction, reducing recombination losses, and developing tandem structures to achieve higher efficiency by combining different types of solar cells.   However, one significant obstacle to their performance is the saturation of the open-circuit voltage at higher light intensities. To optimize the efficiency and overall performance of perovskite solar cells, a comprehensive understanding of these factors becomes essential.

In a groundbreaking study published in the peer-reviewed Journal Advanced Materials Interfaces, Professor Jai Singh and his team of researchers from Charles Darwin University Australia proposed a new analytical expression that directly relates the open-circuit voltage to several key factors. These factors include the quasi-Fermi level splitting, interface energy offsets, and nonradiative recombination losses. The researchers validated their model by comparing it with experimental results.

To calculate the open-circuit voltage of perovskite solar cells, the researchers utilized the drift-diffusion model, which is essential for understanding the mobility of charge carriers within the solar cell. The open-circuit voltage is defined as the voltage at which the net current becomes zero. By analyzing the total current density equation and incorporating the drift-diffusion model, the researchers derived an expression for the open-circuit voltage. This equation takes into account variables such as temperature, recombination rates, carrier concentrations, and carrier mobilities.

The research team discovered that the quasi-Fermi level splitting plays a significant role in enhancing the open-circuit voltage of perovskite solar cells. Increasing the quasi-Fermi level splitting leads to higher open-circuit voltage values. Additionally, minimizing interface energy offsets, which refer to variations in energy levels between different layers of perovskite solar cells, can also increase the open-circuit voltage. By reducing these energy discrepancies, the flux of charge carriers across interfaces can be influenced, thereby enhancing the open-circuit voltage.

Another factor that affects the open-circuit voltage is nonradiative recombination losses. When charge carriers recombine without emitting light, these losses can reduce the quasi-Fermi level separation, resulting in a lower open-circuit voltage. The authors found that by reducing nonradiative recombination losses, the open-circuit voltage can be increased.

To validate their model, the authors applied their newly derived open-circuit voltage equation to two perovskite solar cells with distinct hole transport layers: PTAA and P3HT. The model’s predictions aligned well with experimental results for both types of perovskite solar cells. Specifically, the perovskite solar cells with PTAA as the hole transport layer exhibited a higher open-circuit voltage compared to those with P3HT. This difference can be attributed to variances in band bending and interfacial defects between the two-hole transport layer materials.

In conclusion, Professor Jai Singh and his colleagues demonstrated that increasing quasi-Fermi level splitting, minimizing interface energy offsets, and reducing nonradiative recombination losses can all contribute to an increase in the open-circuit voltage of perovskite solar cells. By applying their model to various perovskite solar cells and comparing the results with experimental data, the authors were able to validate their model and provide additional support for their conclusions.

This research holds significant promise for the further development and optimization of perovskite solar cells. By gaining a deeper understanding of the mechanisms governing open-circuit voltage behavior, researchers can work towards mitigating or eliminating the saturation effect. This, in turn, will lead to improved efficiency and performance, making perovskite solar cells an even more viable and sustainable energy source in the future.